The present invention relates to data protection technology in a computer system.
Needless to say, high availability is required for key public and private sector systems that support the social infrastructure. For this reason, there is the technology disclosed in U.S. Pat. No. 7,043,665 as storage clustering technology that realizes application continuity. In this technology, the identity of data in a first storage apparatus and a second storage apparatus that are used in everyday business operations is assured in accordance with a synchronous remote copy. In a case where a failure is detected in the first storage apparatus by the host that is performing the business operation, the host reconfigures the apparatus address information inside a control block and switches the pointer so as to enable host application input/output to be executed with respect to the second storage apparatus. Further, the control of a synchronous remote copy is also carried out. In accordance with this technology, it is possible to switch over from the first storage apparatus to the second storage apparatus without staticizing the host application, thereby making it possible to enhance the availability of business operations.
In addition to the above, there is demand in the data storage market for a so-called disaster recovery system, which does not lose data even when a storage apparatus storing a large volume of data is destroyed in a disaster or the like. To meet the requirements of such a market, a computer system that uses remote copy technology to backup data is provided. This computer system stores the same data in storage apparatuses that are installed in two very separate locations. When the data of the one storage apparatus is updated, this update is either synchronously or asynchronously reflected in the other storage apparatus in accordance with a remote copy. For this reason, the identity of the data in the two storage apparatuses is assured.
Furthermore, in order to heighten data protection, a computer system that installs storage apparatuses in three mutually separate locations is disclosed in U.S. Pat. No. 7,167,962. In this computer system, the identity of the data in the first storage apparatus, which is used in everyday business operations, and the remotely located second storage apparatus is assured in accordance with a synchronous remote copy. Alternately, the identity of the data in the first storage apparatus and the remotely located third storage apparatus is assured in accordance with an asynchronous remote copy.
In a case where it becomes impossible to use the first storage apparatus for a business operation as the result of a failure caused by a disaster, the second storage apparatus takes over the operations of the first storage apparatus. In a case where the second storage apparatus is also unable to be used at this time, the third storage apparatus takes over the business operations of the first storage apparatus. As a result of this, it is possible to prevent the loss of data even when a serious disaster occurs.
In a computer system that installs storage apparatuses in three locations like this, data is not replicated between the second storage apparatus and the third storage apparatus during normal operation. For this reason, the identity of the data in the second storage apparatus and the third storage apparatus is not guaranteed. Therefore, in a case where a failure also occurs in the second storage apparatus subsequent to the second storage apparatus having taken over the business operations of the first storage apparatus, the third storage apparatus is not able to take over the business operations of the second storage apparatus.
For this reason, the data identity between the second storage apparatus and the third storage apparatus is assured prior to the second storage apparatus commencing operation to take over the business operations of the first storage apparatus. After the second storage apparatus has commenced operation, the data update of the second storage apparatus is reflected in the third storage apparatus in accordance with a remote copy. As a result of this, when a failure occurs in the second storage apparatus, the third storage apparatus is able to take over the business operations of the second storage apparatus.
In a case where all of the data of the second storage apparatus has been replicated in the third storage apparatus at the time of this takeover, the data identity of these storage devices is assured. However, it takes a long time to replicate all the data like this. This can take more than several hours in the large-capacity storage apparatuses of recent years in particular. A case where the second storage apparatus is unable to be used in business operations until all of its data has been replicated raises concerns of serious economic losses being incurred due to the system being suspended for a long period of time. As a technique for shortening the time required to assure the data identity between this second storage apparatus and third storage apparatus, there is the data update method disclosed in U.S. Pat. No. 7,447,855. This technology reduces the amount of data to be replicated when assuring the identity of the second storage apparatus and the third storage apparatus by mutually reflecting the difference data of the one apparatus in the other apparatus, thereby shortening the time required as a result. In this specification, the technology for assuring data identity as described in this U.S. Pat. No. 7,447,855 will be called a “difference resync between secondary volumes”.
In a case where the asynchronous remote copy of U.S. Pat. No. 7,167,962 and U.S. Pat. No. 7,447,855 is applied to the storage clustering technology of U.S. Pat. No. 7,043,665, it is conceivable that the asynchronous remote copy be carried out by regarding the one storage apparatus configuring the cluster as the copy source, but linking cluster control with an asynchronous remote copy for use in disaster recovery does not make it possible for the system to be operated with higher performance or greater reliability.